Here's wishing Kristen Johnston a healthy, happy holiday season! The comedic TV star, 46, revealed via her Facebook page on Tuesday, Dec. 17 that she's been battling a serious health problem for several months -- leading to two weeks at the Mayo Clinic and two missed episodes of her TV Land sitcom The Exes.

"I've been really, really sick since early Sept. Full body muscle weakness to the extent that just walking difficult, stairs impossible and I even need a neck brace to hold my head up," the 3rd Rock from the Sun star writes. "Lying down I'm fine, which is great for writing or killing time on social media (thank you all!!), but it's kind of disastrous when you're in a sitcom that requires tons of physical comedy."

"I didn't mention it because I didn't want people overreacting (on twitter & FB?? NOO!!)," she tells her fans. "I know many of you have experienced similar issues or know people who have, but please try to refrain from diagnosing me. (I do it too!!)"